【作者】 熊震；

【导师】 邵刚勤；

【作者基本信息】 武汉理工大学 ， 材料学， 2007， 硕士

【摘要】 难熔金属碳化物具有高熔点、高硬度、化学稳定性好、导电导热能力强等优点，广泛应用于高速切削工具、耐磨材料、超硬涂层及高温结构材料等方面，还被用作于超细WC-Co硬质合金的抑制剂。难熔金属碳化物由金属钴粘结而成的硬质合金材料具有高硬度和良好的耐磨性，以及高的红硬性。超细WC-Co硬质合金则兼具了高强度、高硬度的“双高”性能，在集成电路板微型钻头、点阵打印机打印针头等方面有着广泛的应用。WC-Co复合粉末因具有成分高度均匀的特性而备受研究者的青睐，开发出适用产业化的制备工艺是20多年来硬质合金工作者们孜孜追求的目标。而成本高、工艺不易控制、环保性不强等缺点一直难以克服。本工作采用溶解性好的偏钨酸铵和环保性强的碳酸钴为基本原料，经喷雾干燥后煅烧得到氧化物粉末，再配以碳黑球磨混匀后于真空炉中在低于1000℃下直接还原碳化，一步得到BET粒径为0.29μm、游离碳含量Cf≤0.06wt.％的超细WC-10wt.％Co复合粉末。氧化物CoWO₄／WO₃在碳化过程中的物相变化为：CoWO₄／WO₃→CoWO₄+WO₂+W₁₈O₄₉→CoWO₄+WO₂+W₁₈O₄₉+W→WC+Co₆W₆C+Co₃W₃C+Co→WC+Co。将所得WC-10wt.％Co复合粉末添加抑制剂（0.4wt.％VC+0.4wt.％Cr₃C₂）后真空烧结并辅以低压热处理，得到WC-10wt.％Co硬质合金。为了探讨粗颗粒WC粉末的添加对超细WC-Co复合粉末烧结合金显微结构和力学性能的影响，将粗颗粒WC粉（FSSS∶0.9μm）和Co粉（FSSS∶1.0μm）（WC∶Co=9∶1，in mass）按质量比分别为30％、50％和70％添加到所制备的WC-10wt.％Co复合粉末中去。结果表明：由含70wt.％（WC-10wt.％Co复合粉末）和30wt.％（90wt.％WC+10wt.％Co粗颗粒粉末）混合粉末制备所得的合金具有最均匀的显微结构和最优异的力学性能。本工作基于在粘结相Co中引入抑制剂（难熔金属碳化物）的设想，采用抑制剂氧化物和Co₃O₄为基本原料，用碳黑进行在真空炉中进行直接还原碳化，分别得到Co-30wt.％VC、Co-30wt.％Mo₂C、Co-30wt.％TaC、Co-30wt.％TiC和Co-30wt.％NbC等钴-抑制剂复合粉末。结果表明：钴的参与能有效降低抑制剂氧化物的碳化温度，所得粉末呈现出典型的核壳型结构。本工作还对钨钴氧化物粉末CoWO₄／WO₃被C的直接还原碳化过程进行了研究，对有钴参与时难熔金属氧化物的低温碳化机理进行了分析，还对超细WC-Co硬质合金的强度和硬度等问题进行了尝试性的探讨。更多还原

【Abstract】 Refractory metal carbides possess of high melting point, high hardness, chemical stability, good electrical conductivity and thermal conductivity, thus are widely used in cutting, wear resistant parts, coating, high temperature structural materials, and grain growth inhibitors for ultrafine WC-Co hardmetals.Hardmetals, consisting of refractory metal carbides cemented by the cobalt phase, exhibit high hardness, wear resistance, and excellent hot hardness. Ultrafine WC-Co hardmetals have been applied in areas such as miniature drills for highly integrated printed circuit boards （PCBs）, pins for dot-printers, and so on, owing to its both high hardness and high strength.WC-Co composite powder has attracted substantial interests due to its uniform distribution in composition, and proper routes suited for industrialization have been exploring by scientists and engineers in recent decades. However, disadvantages such as high cost, inaccurate control industrially, and environment contamination are difficult to conquer with such routes.In this work, ultrafine tungsten carbide-cobalt （WC-10wt. %Co） composite powder was synthesized via spray-drying and direct reduction and carburization process in vacuum, which includes precursor preparation by spray-drying of a suspension of ammonium metatungstate （AMT） and cobalt carbonate （CoCO₃）, calcination to evaporate volatile components, formation of tungsten-cobalt mixed oxide powder （CoWO₄/WO₃）, ball-milling with carbon black, and subsequent direct reduction and carburization reaction in vacuum. The synthesis temperature of WC-10wt.%Co composite powder withoutηor graphite phases is lower than 1000℃. The calculated particle size by BET test is 0.29μm. The carburization process is described as follow: CoWO₄/WO₃→CoWO₄ + WO₂ + W₁₈O₄₉→CoWO₄ + WO₂ + W₁₈O₄₉ + W→WE + Co₆W₆C + Co₃W₃C + Co→WC + Co. Coarse WC powder （FSSS: 0.9μm） and Co powder （FSSS: 1.0μm） （WC: Co = 9: 1 in mass） were added into the obtained WC-10wt.%Co composite powder with addition of 30wt.%, 50wt.% and 70wt.%, respectively. Results show that the hardmetal fabricated from 70wt.% （WC-10wt.%Co composite powder） + 30wt.% （90wt.%WC + 10wt.%Co coarse powder） mixed powders exhibits a fine microstructure as well as optimum mechanical properties.Cobalt-inhibitor composite powders of Co-30wt.%VC, Co-30wt.%Mo₂C, Co-30wt.%TaC, Co-30wt.%TiC and Co-30wt.%NbC were synthesized by direct reduction and carburization process in vacuum, using grain-growth-inhibitor oxides, Co₃O₄, and carbon black as the raw materials. Results show that the carburization temperature can be effectively lowered by the participation of Co₃O₄, and the obtained powders exhibit obvious core/rim structure.The process of direct reduction and carburization is investigated. The low temperature carburization mechanism of refractory metal oxides with the participation of Co₃O₄ is analyzed, and the relationship of hardness and strength is also discussed.更多还原